Glacial-interglacial shifts in dominant climate forcing over the last 33 ka in the northern South China Sea

Abstract. The northern South China Sea is a critical region for understanding East Asian Monsoon dynamics. However, integrated, multi-proxy records elucidating long-term climatic and vegetation changes in this region remain fragmented, with a notable scarcity of coherent land-ocean interaction data during the Last Glacial Maximum (LGM). This gap has impeded progress in elucidating the mechanisms underpinning monsoon variability and in rigorously evaluating the performance of palaeoclimate models. To address this, we conducted a multi-proxy analysis combining palynological, organic- and inorganic-geochemical methods on a marine sediment core from the northern South China Sea to reconstruct environmental and oceanic dynamics at millennial-scale resolution that spans the last 33 ka. Our results reveal a clear contrast between glacial and interglacial conditions and drivers: the glacial period was characterized by higher sedimentation rates, elevated marine primary productivity, cooler climate, lower humidity and herb-dominated vegetation associated with enhanced fire activity in the adjacent terrestrial ecosystems. Deglaciation was characterized by pronounced warming and reduced productivity, together with increased moisture availability, a shift toward pine-dominated vegetation, minimal fire activity, and reduced fluvial input as the coastline retreated. The overall findings highlight a fundamental transition in climatic controls, from a regime dominated by sea level forcing during the glacial period to one increasingly governed by tropical ocean-atmosphere interactions initiated by early ocean warming during the interglacial.